Chamber pressure control using free vortex flow

ABSTRACT

Inlet means supplies a continuous flow of gas with a swirl velocity and at a chosen static pressure to a chamber to establish a free vortex flow therein. Surfaces define an annular path within the chamber that maintains the free vortex flow and guides it toward chamber outlet means. That portion of the chamber not including the annular path becomes pressurized to the supply static pressure of the gas, while the static pressure of the gas within the path changes with its distance from the vortex axis. By properly spacing and locating the inlet means from the outlet means and by properly sizing the annular path, the discharge static pressure of the gas can be controlled.

United States Patent @191 Brown et al.. v

'[ Oct. 30, 1973 CHAMBER PRESSURE CONTROL USING FREE VORTEX FLOW lnventors: Wayne M. Brown, Southwick, Mass; William A. Grace, East Hartford, Conn.

United Aircraft Corporation, East Hartford, Conn.

Filed: Feb. 24, 1972 Appl. No.: 228,848

Assignee:

US. Cl. 415/116, 415/178 Int. Cl. F011! 5/08 Field of Search 415/115, 116, 178;

References Cited UNITED STATES PATENTS 3 1971 McBride ..41s 11s 8/1953 Triebbnigg etal 416/90 2,487,514 11/1949 Boestad et al. 4l5/l 15 Primary Examiner-Henry F. Raduazo AttorneyCharles A. Warren [57] ABSTRACT Inlet means supplies a continuous flow of gas with a swirl velocity and at a chosen static pressure to a chamber to establish a free vortex flow therein. Surfaces define an annular'path within the chamber that maintains the free vortex flow and guides it toward chamber outlet means. That portion of the chamber not including the annular path becomes pressurized to the supply static pressure of the gas, while the static pressure of the gas within the path changes with its distance from the vortex axis. By properly spacing and locating the inlet means from the outlet means and by properly sizing the annular path, the discharge static pressure of the gas can be controlled.

2 Claims, 2 Drawing Figures Patented Oct. 30, 1973 3,768,921

BACKGROUND OF THE INVENTION 1. .Field of Invention This invention relates to establishing a selected static pressure within a chamber while concomitantly providing'a continous flow of gas from said chamber at a different selected static pressure.

2. Description of the Prior Art There are a number of applications wherein it is desirable, if not necessary, to maintain a low pressure at one location within a chamber, and to maintain a high pressure at another location. For example, it may be desirable to maintain a low pressure near a seal for the chamber to prevent gas from leaking out of the chamber; and it may at the same time be required that high pressure air be bledfrom the chamber through holes or other means located in some other area of the chamber. I

For example, some current and most advanced gas turbine engines have extremely high turbine temperature requirements, necessitating the use of hollow turbine blades through which a coolant gas is pumped under pressure. Generally, the coolant gas is discharged into the engine gas stream through holes in the wall of the blade for convectively cooling the external surface of the blade; there is thus a requirement that the pressure of the coolant gas fed into the hollow blade be higher than the dynamic pressure in the gas path. This high pressure coolant gas is often supplied to the blades from a chamber formed between the turbine rotor disc and adjacent stationary structure. Passageways through the disc usually provide communication between said chamber and the hollow blades. A continuous flow of high pressure coolant gas must be fed into the passageways from the chamber. This presents a problem because the chamber formed between the rotating turbine disc and the stationary structure of the engine must be maintained ata relatively low pressure to prevent large amount of air from leaking out of the chamber through seals provided between the rotating structure and the stationary structure as is well known to those knowledgeable-in the turbine art.

One technique which has been used to solve this problem is to construct a second chamber within the first chamber and locating the second chamber at the inlet to said passageways through the disc-High pressure air is pumped into this second chamber, whereupon it is received into the'passageways through the disc and enters the blades. One difficulty with this technique is that it requires an elaborate sealing system between the two chambers; this is often impractical, if not impossible to accomplish because of the small area within which the second chamber and sealing system must be located.

A second possible solution is to expand high pressure air through a plurality of axially directed nozzles to a low pressure within the first chamber; to pass said low pressure air through a conventional axial diffuser to recover pressure; and then, in some manner, to duct the now high pressure air to the passageways through the disc. The undesirable feature of this system is the tremendous losses associated with the diffusion process and the changing of the direction of the supply of cooling air from axial to radial for bringing it into the blades; also, since the cooling air has little or no tangential velocity with respect to the disc, the disc must work on the air to bring it up to disc velocity at the entrance to the passageways through the disc; this, of course, is wasted turbine work. Also, because of the losses associated with bringing the air from the nozzles to the passageways, a greater amount of air must be pumped through this system to achieve the same amount of blade cooling than would otherwise be required if such losses were not present.

SUMMARY OF THE INVENTION According to the present invention, a chamber having distinct first and second portions is provided with inlet means for discharging gas into the chamber with a swirl velocity and at a chosen static pressure in a manner so as to establish a free vortex flow therein, outlet means suitably spaced from said inlet means, and surfaces defining a suitable path within the second portion of the chamber for maintaining the free vortex flow and for leading it from the inlet means to the outlet means, the free vortex flow arriving at the outlet means at a different chosen static pressure.

In one embodiment, the inlet means includes nozzle means, and a swirl velocity is imparted to the gas by arranging the nozzle means about a circumference and discharging the gas from the nozzle means substantially tangentially to said circumference. The swirling gas will flow toward the outlet means as a free vortex along the provided path either losing or recovering static pressure depending on whether the outlet means are spaced radially inward from or radially outward from the nozzle means, respectively, as the case may be. By properly choosing the radial distance between the inlet and outlet means the desired static pressure change may be accomplished. Furthermore, the present invention requires that to maintain the free vortex flow the radial velocity of the gas within the free vortex, as it flows from the inlet means to the outlet means, must be within a certain range relative to the tangential velocity of the gas; this maybe accomplished by properly sizing the axial dimension of the .path which the gas follows.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partlyv sectioned, side elevation view of a turbine rotor and front seal assembly which uses one embodiment of the invention; and

FIG. 2 is'a developed partial sectional view taken along the line 22 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Consider, as an example of one application of the present invention, the requirement of providing a substantial flow of cooling air under high pressure to a plurality of hollow turbine blades 10 (FIG. 1) circumferentially spaced around the periphery of a turbine disc 12. Commonly, the cooling air is brought into the blades 10 through passageways 16 in the disc 12 which communicate with inlets'18 to the hollow blades 10. In this instance, the passageways 16 have their inlets 20 on the forward side 22 of the disc 12. The cooling air is pumped through the blades and is then exhausted into the gas path 23 through holes (not shown) in the blades; thus, the pressure of the air being pumped into the blades must be higher than the dynamic pressure of the working fluid in the gas path.

As is well known in the gas turbine art, any leakage of the hot, high pressure working fluid from the gas path 23 into the area on the forward side 22 of the disc 12 must be prevented; therefore, a minimum amount of leakage into the gas path is desired. Also, a high pressure load on the forward side 22 of the disc might upset the thrust balance of the engine. It thus follows that the static pressure on the forward side 22 of the disc 12 should be slightly higher than the static pressure in the gas path 23.

In the present instance, this is accomplished by forming a sealed annular chamber 25 on the forward side of the disc. The chamber 25 comprises a rotating portion and a stationary portion. The rotating portion comprises the disc itself and inner and outer knife edge seals 30, 40, respectively, of well known configuration, attached to the disc by suitable means such as bolts 42, 44, respectively. The stationary portion is mounted on an axially extending casing 52 and comprises a conical wall 56, and inner and outer seal lands 58, 60, respectively. The conical wall 56 is attached to the casing 52 by suitable means such as a tongue and groove arangement 62 and extends radially inwardly and rearwardly therefrom. At the rearward end 64 of the wall 56 is a radially inwardly extending flange 66; extending rearwardly from the flange 66 and attached thereto by suit able means such as bolts 68 is the inner seal land 58 which is in sealing relation 'with the inner knife edge seal 30. Extending radially inwardly from the casing 52 but downstream from the tongue and groove 62, is a flange 70; extending rearwardly from the flange 70 and attached thereto by suitable means such as bolts 72 is the outer seal land 60 which is in sealing relation with the outer knife edge seal 40. In this embodiment the inlets 20 to the passageways 16 also serve as outlets for the chamber 25 and are hereinafter referred to as such.

Coolant gas, at a total pressure higher than the static pressure in the gas path 23 and from a suitable source such as a compressor (not shown), is introduced into an annular plenum 90 through as plurality of circumferentially spaced holes 92 through the casing 52. The plenum is formed between the conical wall 56 and a second conical wall 94 rearwardly spaced from the wall 56 and attached to the casing 52 at the flange 70 by suitable means such as bolts 72. The coolant gas is thereupon expanded into the chamber 25 to a lower static pressure than existed in the plenum and to a high velocity through nozzle means, such as a row of vanes or, as shown in FIG. 1, a plurality of tubular nozzles 100 circumferentially spaced within the chamber about the engine axis (not shown) and in communication with the plenum 90. Said lower static pressure is the pressure desired within the chamber in the vicinity of the seals 30, 40 to minimize leakage. Since the chamber 25 is sealed, the path of least resistance for the gas discharged from the nozzles 100 is toward the chamber outlets 20, from whence it can easily escape the chamber; the gas will travel from the nozzles 100 to the chamber outlets wherever they may be located.

When the coolant gas arrives at the chamber outlets 20 its static pressure must be higher than the dynamic pressure in the gas path 23; to minimize leakage it is also necessary that the static pressure within the chamber 25 in the vicinity of the seals 30, 40 be slightly higher than the static pressure in the gas path 23; and finally, to minimize the required amount of coolant gas flow, it is desired that there be a minimum of lost energy as the coolant gas travels from the nozzles 100 to the chamberoutlets 20. This may be accomplished by means of a properly confined free vortex flow (hereinafter explained) of the gas from the nozzles to the chamber outlets by a substantially direct path, which is preferably a radial path. The gas will lose velocity and recover static pressure within the path in a determinable manner as it travels along the path so that if the nozzle exits 101 are radially spaced from the chamber outlets 20 by the properdistance, then a desired static pressure can be established at the chamber outlets 20.

The free vortex is established by discharging the coolant gas from the nozzles 100 in a direction substantially tangential to the circumference about which the nozzles are spaced. As seen in FIG. 2, the nozzles 100 in this embodiment are directed approximately 15 downstream (to the right in FIG. 1); this is done because of the close proximity of adjacent nozzles with the result that if they were directed tangential to a circle having that same axis as the engine, then the gas being discharged from each nozzle would hit the nozzle immediately in front of it. Although any axial component of flow velocity imparted by the nozzles 100 is wasted energy and should be minimized, 15 is small enough so as not to be of any serious consequence. Minimizing energy loss also suggests that the nozzle exits 101 be located, as nearly as possible, at the same axial location as the chamber outlets 20 to minimize axial travel of the gas flow.

A free vortex is a rotational flow wherein the vorticity is zero everywhere except at the center of rotation,

and the following formula is applicable:

V r C where V, equals the tangential velocity of the gas; r equals the radial distance from the center of rotation; and C is a constant. This is known as the equation of a free or simple vortex. If the radial velocity V,. of the gas is small in comparison to the tangential velocity, then the pressure at any point within the free vortex can be expressed as follows:

fluid, such as a gas, according to the following equation:

P= I/ I where P,- is the static pressure of the gas; R is the universal gas constant; and T is the static temperature of the gas as given by the following equation:

where T is .the total temperature of the gas, a constant; J is the mechanical equivalent of heat; C,I is the gas specific heat at constant pressure; and the other terms are as previously defined.

Equations (1), (2), (3), and (4) can be combined to give the following equation which represents a ratio of two static pressures within the free vortex:

where the subscript 1 denotes a condition at a radius r,; the subscript 2 denotes a condition at a radius r k is the ratio of specifc heats for the gas, C,,/C,, (which is 1.40 for air); and M, is the tangential mach number of the gas at r and is defined by the well known formula:

where all the terms are as previously defined.

Equation (5) can be rewritten into a more convenient form as follows:

page) P From Equation (5a) it can be seen that if r P, M, and k are known then r can be calculated. In other words if r is the radial location of the chamber outlet means (such as and if P, and M, are conditions of the nozzle exits (such as 101) then r,, the radial location of the nozzle exits, can be calculated which will result in a pressure P at the outlet means. It must be kept in mind that equation (5a) is valid only for perfect free vortex flow, and cannot be depended upon for accurate results unless the radial velocity of the gas is small in comparison to the tangential velocity, as it would be if it meets the criteria hereinafter discussed.

From Equations (1) and (2) above, it can be seen that as the gas moves radially away from the engine axis, its tangential velocity decreases and its staticpressure increases. In the limit, asr becomes very large, the

static pressure P, will equal the total pressure Pf. The

important feature of this phenomenon, from the point of view of the present invention, is that the static pressure rise occurs only within the boundaries of the free vortex flow of coolant gas; that is, with reference to the preferred embodiment, if the free vortex flow from the nozzles 100 is properly confined to travel wholly within a distinct portion of the chamber then the static pressure of the remaining portion of the chamber 25(near the seals 30, will be substantially the gas discharge static pressure at the nozzle exits 101 (P5 ln the present example, an annular path 118, defined by the rear surface 119 of a conical seal support 120 and the forward surface 22 of the disc 12, confines and directs the coolant gas from the nozzle exits 101 to the chamber outlets 20. The pressure rise occurs only within this path.

In the general case, the chamber outlet means can be located radially inwardly of the nozzle means as well as radially outwardly as in the above preferred embodiment; the gas being discharged from the nozzle means will follow the path of least resistance in seeking its way out of the chamber. Thus, the free vortex may move radially inwardly and radially outwardly depending on the location of the outlet means. Equations (1 and (2) above indicate that when the gas moves inwardly static pressure is lost rather than recovered. In that instance, the static pressure within the chamber will be higher than the static pressure of the gas. at the outlet means. This might be desirable for some applications.

As hereinabove mentioned, for afree vortex flow to exist, Equation (1) above must be applicable. It becomes apparent from this equation, that if anything interferes with the tangential velocity of the gas within the swirling flow, then the free vortex may be disrupted. There are three items of major concern in this regard. The first is that there can be no obstructions within the radial path of the gas which would affect the tangential velocity; second, because gas may be discharged from nozzles as a plurality of discrete streams (as in the preferred embodiment) there may be viscous drag effects between adjacent streams which may be disruptive; and third, if the axial dimension of the annular path becomes too narrow, then the free vortex flow may be disrupted by boundary layer effects along the side walls of the path.

The first of the above considerations needs no explanation. The second and third considerations are both related to the radial velocity of the gas during free vortex flow. The radial velocity of the gas at any particular radius may be expressed in terms of the followingequation:

V (m/Z'n'rWp) where V, equals the radial velocity; m equals the mass flow of gas, a constant; r equals the radius from the center of rotation; W equals the axial width of the path at r; and p equals the density of the gas at r as defined by formula (3) above. The term 2 1rrW is simply the crosssectional area of the radially outward flow at a radius Returning now to the second of the above considerations, the effects of viscous drag between adjacent streams of gas is dependent on teh tangential'velocity of the gas and the length of time over which this drag force acts; the time factor is directly dependent upon the radial velocity of the gas, which determines how long the gas remains within the chamber. If the radial velocity of the gas at a particular radius is at least 0.01 times the tangential velocity of the gas at that radius then the viscous drag effects will not be significantly disruptive. Since, from Equation (1) above, the tangential velocity at any radius is known, then from Equation (7) an acceptable radial velocity can be established by properly choosing the axial width W of the path. The above criteria places a maximum permissible width on the path.

Regarding the third consideration boundary layer effects it is apparent that a free vortex flow through an annular path, such as the path 118, may be disrupted by boundary layer effects if the axial width W becomes too narrow (see Equation (7)). It is desirable that the radial velocity of the gas be less than 0.1 times the tangentialvelocity to assure that the width W of the radial path does not become too narrow and the boundary layer formed on the walls of the path does not disrupt the free vortex flow. The above criteria thus dictates the minimum width of the radial path. It should be mentioned at this point that a radial velocity greater than 0.1 times the tangential velocity, such as 0.5 times the tangential velocity, may also be satisfactory, however, a radial velocity less than O.l times the tangential velocity is preferredThus, by properly sizing the annular path, the free vortex may be maintained.

Heretofore, this invention has been described without reference to the fact that walls 22, 120 of the path 118 rotate. The reason for thisis that rotation is not needed to obtain the desired free vortex flow with its attendant pressure recovery. This is apparent from the above formulas. However, it is well known in the turbine art that unless the coolant gas at the chamber outlets 20 has a tangential velocity component which is in the same direction and at least as large as the tangential velocity of the disc 12 at the outlets 20 then the disc 12 will have to do work on the air to bring the air into passageways l6; conversely, if the tangential velocity of the gas is higher than the tangential velocity of the disc at the outlets 20, and is moving in the same direction as the disc 12, then the coolant gas actually does work on the disc as it enters the passageways 16. This fact provides good reason for recovering only that amount of pressure required to insure a continuous flow of coolant gas through the blades 10, because a further increase in the pressure would result in a further reduction in the tangential velocity of the gas. Furthermore, as pressure increases, gas temperature increases which is of course undesirable if the gas is to be used for cooling as in the present embodiment.

An inherent advantage resulting from the rotation of the walls 120, 22 where rotation of the gas and the walls is in the same direction, is that boundary layer build-up along the walls may be reduced. This advantage becomes more important as the axial width of the path 118 becomes narrower.

As a specific example of the application of the above equations consider the configuration shown in FIG. 1. The dynamic pressure of the working fluid in the gas path is 270 psi; the static pressure is 225 psi. It is desired that the static pressure at the inlets 20 to the'passageways 16 be 284 psi (P which is higher than the dynamic pressure in the gas path; and it is desired that the static pressure within the chamber 25 near the seals 30, 40, be 252 psi (P which is higher than the static pressure in the gaspath. The chamber outlets 20 are located at a radius (r:) of 14.0 inches. Cooling air at a total pressure of 323 psi and total temperature of l,080F is received into the plenum 90 whereupon it is diffused through the nozzles 100 into the chamber 25 to the desired static pressure of 252 psi. The tangential velocity of the cooling air at the exits 101 of the nozzles 100 is 1,080 feet per second as can be determined from formulas (2), (3) and (4). Equations (2), (3) and (4) can also be solved for T,; then equation (6) can be solved for M finally equation (a) can be solved for r the radial location of the nozzles needed to obtain a static pressure of 284 psi at the chamber outlets 20, which in this example calculates to 10.0 inches. Also, in this example the air is discharged from the nozzles 100 at a mass flow rate of 10.0 pounds per second which, it has been determined, is the minimum flow needed to provide sufficient cooling to the blades 10. Knowing this flow rate, Equation (7) can be used to establish the radial velocity of the cooling air. in this embodiment the axial width of the radial path is varied between 1.0 inch at a radius of 10.8 inches, to 0.5 inch at a radius of 14.0 inches, to produce a radial velocity which varies between 45 to 65 feet per second, which is on the order of 0.05 times the tangential velocity.

Although the preferred embodiment hereinabove described uses a plurality of circumferentially spaced nozzles to establish the free vortex flow within the chamber, actually any chamber inlet means capable of establishing a swirling flow may be suitable. That is, the swirl may be put into the gas external of the chamber and be simply introduced into the chamber through suitable inlet means such as a full annulus. Also, there need not be a plurality of chamber outlets; there may be only one outlet and that outlet may be, for example, an annulus surrounding the axis of rotation of the free vortex flow.

It should be understood by those skilled in the art that various other changes and omissions in the form and detail of the invention may be made without departing from the spirit and the scope of the invention.

Having thus described typical embodiments of our invention, that which we claim as new and desire to secure by Letters Patent of the United States is:

1. In a gas turbine engine having an axis, a turbine rotor disc, and stationary structure adjacent said turbine rotor disc, said stationary structure communicating with said disc to form an annular chamber therebetween, the chamber having distinct first and second annular portions in gas communication with each other, the second portion being spaced radially outwardly of the first portion and including chamber outlet means located at a radius r from the engine axis, the disc having a plurality of hollow blades circumferentially spaced about the periphery thereof, means for providing cooling air at a static pressure P, within the first portion of the chamber and a continuous flow of the cooling air at a static pressure P from said chamber outlet means into the blades, wherein P, is higher than P comprising, in combination with the chamber:

' nozzle means for supplying a continuous flow of cooling air into the first portion of the chamber, said nozzle means circumferentially disposed about the engine axis within the first portion of the chamber at a radius r, given by the following equation:

said nozzle means being directed substantially tangentially to the circle about which said nozzle means is spaced, where P, is the static pressure of the cooling air supplied by said nozzle means, M is the tangential mach number of the cooling air supplied by said nozzle means, and k is the ratio of specific heat for said cooling air, said chamber including axially spaced radially extending surfaces disposed radially outwardly of said nozzle means and defining an obstruction-free annular path substantially axially aligned with said nozzle means and leading from said nozzle means substantially perpendicularly away from said axis to said outlet means for carrying the cooling air from said nozzle means to said outlet means and dimensioned so that the radial velocity of the cooling 'air at each radial location within the path is greater than 1 percent of the tangen- 10 circumferentially spaced passages through said disc from said surface to said blades, said annular path being dimensioned so that the radial velocity of the cooling air at each radial location within the path is within the range of 1-10 percent of the tangential velocity of the gas within the path at said radial location.

" 9 UNITED STATES PATENT OFFICE (5/54) CERTIFICATE OF CORRECTION Patent No. 3,768,921 Dated October 973 Inventor(s) Wayne M. Brown and William A. Grace It is certified that error appears in the above-identified patent and that said Letters latent are hereby corrected as shown below:

Column 1, line 41 "amount" should be --emounts- Column 3, line 41 "as" should be --a-- Column 4, line 19 after "directed" insert --exactly-- Column 4, line 50' x "presssure" should be --pressure-- Column 6, line 3 change "and" to or Column 6, line 45 "teh" should be "the Signed and sealed this 2nd day of April 1972+.

(SEAL) Attest:

EDHARD 14.1 GHERJR. c G, MARSHALL DANN Attesting Officer Commissioner of Patents 

1. In a gas turbine engine having an axis, a turbine rotor disc, and stationary structure adjacent said turbine rotor disc, said stationary structure communicating with said disc to form an annular chamber therebetween, the chamber having distinct first and second annular portions in gas communication with each other, the second portion being spaced radially outwardly of the first portion and including chamber outlet means located at a radius r2 from the engine axis, the disc having a plurality of hollow blades circumferentially spaced about the periphery thereof, means for providing cooling air at a static pressure Ps within the first portion of the chamber and a continuous flow of the cooling air at a static pressure Ps from said chamber outlet means into the blades, wherein Ps is higher than Ps , comprising, in combination with the chamber: nozzle means for supplying a continuous flow of cooling air into the first portion of the chamber, said nozzle means circumferentially disposed about the engine axis within the first portion of the chamber at a radius r1 given by the following equation:
 2. The apparatus according to claim 1 wherein one of said radially extending surfaces is a surface of said disc and said passageway means includes a plurality of circumferentially spaced passages through said disc from said surface to said blades, said annular path being dimensioned so that the radial velocity of the cooling air at each radial location within the path is within the range of 1-10 percent of the tangential velocity of the gas within the path at said radial location. 